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Arc Flash Energy in Medium vs Low Voltage Systems
2

Arc Flash Energy in Medium vs Low Voltage Systems

Arc Flash Energy in Medium vs Low Voltage Systems

(OP)
I've noticed in some fault current and arc flash studies I've seen lately, that the low voltage systems produced higher incident energies (cal/cm2) than those for medium voltages of similar power levels. My sample size is probably just too low and I know that it is probably quite complex. I am talking about different systems, not the same system with upstream and downstream medium and low voltage interconnected systems.

I've tried to research this a bit, but for example the IEEE-1584 equations are a bit too complex for me to see any clear cut differences. But, does the fault current have a greater effect than system voltage? Will a low voltage system with nine times lower voltage but 9 times higher fault current typically have higher arc flash numbers?

Thanks in advance for any help.

RE: Arc Flash Energy in Medium vs Low Voltage Systems

Voltage plays almost no part; current and time are essentially the only factors.

RE: Arc Flash Energy in Medium vs Low Voltage Systems

Arcing current is a function of voltage, conductor gap, enclosure type, and most importantly, the bolted fault current.

Clearing time is a function of the arcing fault current and the protective device time-current characteristics.

Arc flash energy is a function of clearing time and arcing current.

It is very common to see higher arc flash energies on LV systems, most notably directly downstream of a transformer where the protective device is the transformer primary protection.

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